Th present invention relates to improvements in photoelectric intruder detection systems. More specifically, this invention relates to an apparatus for facilitating the installation of such systems.
For many years photoelectric intruder detection systems of the so-called "electric eye" variety have been relied upon for detecting unauthorized entry in regions under surveillance. Such systems typically comprise a transmitter for transmitting a beam of electromagnetic radiation, usually infrared radiation, through a region in which intrusion is to be detected, and a radiation-sensitive receiver remotely positioned relative to the transmitter in the beam of energy transmitted thereby. An interruption in the beam, such as produced by a person passing through it, causes the energy reaching the receiver to drop below a predetermined threshhold, the result being the sounding of an alarm. A variation of the conventional two-terminal electric eye is the single terminal system in which the transmitter and receiving elements are contained in a single housing. Such a system utilizes a reflector remotely positioned relative to the transmitter/receiver housing to return energy emanating from the transmitter to the receiver.
In the installation of electric eye-type intruder detection systems, one of the major installation problems is determining whether the installation has adequate margin, i.e., whether the system will continue to have sufficient signal under conditions of slight misalignment, vibration, dust build up and (for long installations) fluctuations due to thermal gradients. It is desirable in any electric eye installation to have a margin of at least a factor of two and, more commonly, a factor of four. This large margin helps to prevent false alarms due to slight misalignments, dust and dirt buildup, as well as thermal turbulence. Most electric eye installations contain a meter which indictes to the installer that there is a sufficient signal (beam intensity) for the device to function. In some cases, the meter indication is directly proportional to the signal strength; in others, it is simply an indication that the alarm relay is energized, a condition indicative of adequate signal return. Aside from using a meter or oscilloscope to actually observe internal signals, the most common way for the installer to measure margin is to partially block off a transmitting or receiving lens or, in the case of a reflection type single terminal system, to partially ask the reflector. The problem with masking a lens or a reflector element is that, very often, the light is not evenly distributed over the area of the lens, or reflector; this is especially true for the transmitting lens. Therefore, even though half of the lens or reflector may be covered, the amount of attenuation could be either less than or greater than 50%. Furthermore, it is difficult to judge by eye when a desired portion of a lens or reflector has been obscured.